SHELL-DERIVED RADIOCARBON EVIDENCE REVEALS CHANGING INFLUENCE OF SLOPE WATER CURRENTS TO THE GULF OF MAINE (NORTHWESTERN ATLANTIC) IN RECENT CENTURIES (Invited Presentation)

In order to assess the variability in the local marine radiocarbon reservoir offset (ΔR) and to document relative changes in slope water contributions (Labrador Current versus Gulf Stream) in the Gulf of Maine, we constructed a multi-century master shell chronology from the long-lived ocean quahog (Arctica islandica). The statistically robust and highly synchronous master shell chronology facilitated the reconstruction of a ΔR time series prior to the radiocarbon bomb-pulse of the 1950s, which revealed a highly variable ΔR (103 ± 77) from AD 1760 to AD 1950. The results from the absolutely-dated master shell chronology indicate that using a constant ΔR value to constrain marine sediment age/depth models via radiocarbon in the Gulf of Maine is invalid. In the early part of the record (AD 1760 to AD 1850), the relatively low ΔR values are most consistent with a dominant Gulf Stream source, while after AD 1850 the relatively high ΔR values are consistent with a source derived from the cold and deep Labrador Current. The inferred oceanographic evolution in the Gulf of Maine during this interval will be discussed.